1. Field of the Invention
The present invention relates generally to sewing machines having rotatable sewing heads and methods of controlling the operation of the sewing machines and, more particularly, to a sewing machine which is configured such that a sewing head rotates when an object, such as an airbag, a bag, a shoe, etc., is being sewn so that the sewing operation can be satisfactorily conducted without causing a hitch stitch, and in which a plurality of sewing heads may be arranged on a front surface of an upper beam in a row or, alternatively, a plurality of groups of sewing heads may be provided so as to be independently operable on individual work areas, so that not only the quality of the products can be enhanced but also the productivity can be markedly enhanced, and a method of controlling the operation of the sewing machine.
2. Description of the Related Art
Generally, objects, such as airbags, bags, shoes, etc., are made of comparatively thick materials and have many sewing lines, such as circular, curved, slanted lines, etc., which are difficult to sew. Thus, in the case of conventional sewing machines, hitch stitches were easily formed with respect to a correct sewing direction. Such hitch stitches make the entire stitch shape uneven, thus deteriorating the quality of the product.
FIG. 1 illustrates an embodiment of a conventional sewing machine. In the conventional sewing machine, an arm part 40 having a head unit is disposed on a table 10. A bed unit (not shown) having a hook is disposed under the table 10. A connection unit 60 connects the arm part 40 to the bed unit. An object that is supported by a sewing frame 50 is sewn by interaction between the head unit and the hook of the bed unit.
In the sewing machine having the above construction, the sewing frame 50 can be moved in an X-axis or Y-axis direction by the arm-bed structure, thus making it possible to sew a limited area of an object.
However, in the conventional sewing machine, the sewing frame 50 linearly moves in the X-axis or Y-axis direction. Therefore, when the sewing machine forms a curved, circular or slanted stitch line, hitch stitches are caused in some sections.
FIGS. 2A through 2C are views showing examples of hitch stitches caused in the conventional sewing machine. In the case of a rhombic or rectangular shape, two sides of the four sides were P (Perfect stitch) sections, another side was an H/P (Hitch/Perfect stitch) section where there are normal stitches and abnormal stitches together, and the other side was an H (Hitch stitch) section.
FIG. 2C is an H-P stitch distribution chart by section after sewing. In the case of a circular stitch section, a P (Perfect stitch) section and an H (Hitch stitch) section were in a ratio of almost 1:1:
Therefore, a sewing machine which can realize perfect stitching over the entire section is required in order for the quality of the sewing to be high quality.
Furthermore, the conventional sewing machine cannot process a comparatively large object because the sewing area of the sewing machine is restrictive. To solve this problem, it is required to increase the size of the sewing machine. As a result, a new concept is needed for a sewing machine so that the space required to install a large sewing machine can be minimized.
In addition, the conventional sewing machine can process only one object at a time. Thus, it takes too long to process a large number of objects. Therefore, to enhance the productivity, a sewing machine which can process a plurality of objects at a time is needed.